Physical Landscapes UK: Coastal Landscapes and Processes Flashcards
Coast
Where the land meets the sea
How do waves form?
Wind blows over surface of sea —> friction is created, producing a swell in the water
The size of waves depend on:
- The fetch (how long wave has travelled)
- Strength of wind
- How long wind has been blowing for
Why do waves break?
1) Waves start out at sea
2) As waves approach shore, friction slows base of waves
3) This causes orbit of waves to become elliptical until the crest of the wave breaks over
Constructive waves:
- formed by storms hundreds of miles away
- strong swash + weak backwash
- strong swash brings sediments to build up the beach
- backwash is not strong enough to remove the sediment
- waves are low + further apart
- break gently
Destructive wave:
- formed by local storms close to coast
- weak swash + strong backwash
- strong backwash removes sediment from the beach
- waves are steep and close together
Weathering
The weakening or decay of rocks in their original place on, or close to, the ground surface. This is usually caused by weather factors such as rainfall and changes in temperature
An example of weathering is mechanical weathering:
Freeze-thaw weathering:
1) water collects in rock crack
2) water freezes + expands, widening crack
3) ice thaws + contracts, so water gets deeper into cracks
4) repeated expansion + contraction —> until rocks split
An example of weathering is chemical weathering:
Carbonation:
Acidic rainwater reacts with CaCO3 in rocks to dissolve it —> cracks in the rocks expand
An example of weathering is biological weathering:
Roots get into small cracks in rock
As the roots grow, cracks become larger
This weakens structure of rock until it breaks away
Burrowing animals also break up rock
Mass movement
The downward movement or sliding of material under the influence of gravity
An example of mass movement is a landslide:
Large blocks of rock slide downhill, usually when rock is saturated
*after heavy rainfall
An example of mass movement is a mudflow:
Saturated soil flows down a slope + there is not enough vegetation to hold the soil in place
*after heavy rainfall
An example of mass movement is a rotational slip:
Saturated soil slumps down a curved surface, usually under the influence of gravity
*after heavy rainfall
E.g. Barton-on-Sea, Dorset Coast
How are headlands and bays formed?
1) Waves attack a discordant coastline (alternating bands of hard + soft rock)
2) Softer rock is eroded by sea much quicker, forming a bay
3) More resistant rock is left jutting out into sea - this is a headland and is more vulnerable to erosion
* concordant coastlines (same type of rock) have fewer headlands + bays
E.g. Studland Bay and Durlston Head, Dorset Coast
Erosion
The wearing away of rock along the coastline
Destructive waves are responsible for erosion on the coastline. There are four types of erosion:
ABRASION
Sediment in waves grind down cliff surfaces like sandpaper
Destructive waves are responsible for erosion on the coastline. There are four types of erosion:
ATTRITION
Waves smash rocks and pebbles on the shore into each other, and they break and become smoother
Destructive waves are responsible for erosion on the coastline. There are four types of erosion:
SOLUTION
Acids in sea water dissolve certain types of rock (e.g. chalk or limestone)
Destructive waves are responsible for erosion on the coastline. There are four types of erosion:
HYDRAULIC ACTION
The sheer power of the waves as they smash against the cliff
Air becomes trapped in the cracks in the rock and causes the rock to break apart
There are different types of transportation…SUSPENSION
fine light material is carried along in the water
There are different types of transportation…SOLUTION
minerals are dissolved in the water and carried along in solution
There are different types of transportation…TRACTION
large boulders and rocks are rolled along the river bed
There are different types of transportation…SALTATION
small pebbles and stones are bounced along the river bed
There are different types of transportation…LONGSHORE DRIFT (LSD)
The zigzag movement of sediment along the coastline:
- Swash moves up beach at angle of prevailing wind, so carries sediment up the beach at an angle
- Backwash moves sediment down the beach at 90 degrees to coastline due to gravity
- Zigzag movement transports material along beach
Deposition
Material being transported by the sea is dropped when the wave loses energy
Deposition can occur on coastlines that have constructive waves
Factors leading to deposition include:
- waves starting to slow down + lose energy
- shallow water
- sheltered areas, e.g. bays
- little or no wind
- waves carrying lots of material
How are caves made?
When waves force their way into cracks on the cliff face
How are arches made?
The cave can eventually break through the other side, forming and arch
E.g. Durdle Door, Dorset Coast
How are stacks made?
An arch will gradually become bigger until it collapses. This leaves a headland on one side and a stack on the other
E.g. Old Harry, Dorset Coast
How are stumps made?
The stack will be eroded at the base until it collapses to form a stump
How is a wave-cut notch and platform made?
1) weather weakens top of cliff
2) sea attacks base of cliff, forming a wave-cut notch
3) notch increases in size, causing cliff to collapse
4) backwash carries rubble towards the sea, forming a wave-cut platform
5) process repeats and cliff continues to retreat
E.g. Washing Ledge, Dorset Coast
Formation of beaches
Beaches are formed from deposits of sediment from elsewhere deposited by constructive waves.
Sandy beaches usually found in bays where water is shallow + waves have less energy
Pebble beaches often form where cliffs are being eroded, + where there are higher energy waves
Spit
An extended stretch of sand or shingle jutting out into the sea from the land
E.g. Spurn Head, Holderness Coast
How are spits formed?
•Swash moves up beach at angle of prevailing wind
•Backwash moves down beach at 90 degrees to coastline due to
gravity
- Zigzag movement (LSD) transports material along beach
- Deposition causes beach to extend until reaching a river estuary
- Change in prevailing wind direction forms a hook at end of spit
- Sheltered area behind spit encourages deposition and salt marshes form
Bar
When a spit grows across a bay + joins two headlands together, trapping behind it a shallow lake (lagoon)
Sand dunes
Small hills of sand found at the top of a beach, above the high tide mark, shaped by wind direction and covered in vegetation
E.g. Studland, Dorset Coast
How are sand dunes formed?
1) Material is deposited at a constructive coastline.
2) Wind blows material over the beach and gets trapped around an object (e.g. driftwood).
3) This creates a small mound known as an embryo dune.
4) Over time the sand dunes become bigger and become known as fore dunes, yellow dunes, grey dunes.
5) The largest dune is called a mature dune. It becomes stabilised by vegetation such as marram grass.
Hard engineering
Building artificial structures which try to control natural processes
Coastal management hard engineering method: SEA WALLS
Concrete walls placed at the foot of a cliff to prevent erosion. They are curved to reflect the energy back into the sea.
Pros and cons of SEA WALLS
+ Effective at protecting the base of the cliff
+ Lasts 100 years
- Expensive to build and maintain
- Can erode over time from powerful waves
Coastal management hard engineering method: GROYNES
Wooden or rock structures built out at right angles into the sea.
Pros and cons of GROYNES
+ Builds a beach, which encourages tourism
+ Traps sediment being carried by longshore drift
- By trapping sediment it increases erosion in beaches further down the coastline
- They look unattractive
Coastal management hard engineering method: ROCK ARMOUR
Large boulders placed at the foot of a cliff. They break the waves and absorb their energy.
Pros and cons of ROCK ARMOUR
+ Cheaper than a sea wall and easy to maintain
+ Can be used for fishing
- Looks different from local geology, as the rock is imported from other areas
- The rocks are expensive to transport
Coastal management hard engineering method: GABIONS
Rocks held in mesh cages and placed in areas affected by erosion.
Pros and cons of GABIONS
+ Cheap - approximately £100 per metre
+ Absorbs wave energy
- Not very strong
- Looks unnatural
Soft engineering
Smaller, more environmentally-friendly methods that work with natural processes to manage the coast
Coastal management soft engineering method: BEACH NOURISHMENT
Sand from the seabed is pumped onto an existing beach to build it up.
Pros and cons of BEACH NOURISHMENT
+ Blends in with the existing beach
+ Larger beaches appeal to tourists
- Needs to be constantly replaced
- Kills marine life from seabed
Coastal management soft engineering method: BEACH PROFILING
The sediment is redistributed from the lower part of the beach to the upper part of the beach.
Pros and cons of BEACH PROFILING
+ Cheap and simple
+ Reduces the energy of the waves
- Bulldozers are used but are noisy and disrupt wildlife
- Needs to be repeated continuously
Coastal management soft engineering method: DUNE REGENERATION
Creating or restoring sand dunes to act as a buffer between the land and sea. Marram grass planted on sand dunes stabilises the dunes and helps to trap sand to build them up.
Pros and cons of DUNE REGENERATION
+ Absorbs wave energy
+ Relatively cheap and maintains a natural-looking coastline
- Can be damaged by storm waves
- Areas have to be zoned off from the public, which is unpopular
Coastal management soft engineering method: MANAGED RETREAT
Controlled flooding of low-lying coastal areas if an area is at high risk of erosion. It usually occurs where the land is of low value, e.g. farm land.
Pros and cons of MANAGED RETREAT
+ Cheaper than paying for sea defences
+ Creates a salt marsh which can provide habitats for wildlife and a natural defence against erosion and flooding
- Land is lost as it is reclaimed by the sea
- Landowners need to be compensated
Coastal management case study: Holderness Coast
Location and Background
- Located in east coast of Yorkshire
- Town is popular sea resort for tourists to visit all year round
- Fastest eroding coast in Europe at 1.8m on average each year
Coastal management case study: Holderness Coast
Geomorphic Processes
- Flamborough Head in north of HC exposed to cliff retreat - cliff will eventually collapse
- LSD travels from north of Mappleton - groynes in place have reduced sand south of groynes, increasing rate of erosion there
- Spurn Point (spit) at south of HC was created by LSD
Coastal management case study: Holderness Coast
Management
- HC protected by number of groynes —> trap sand + build up beach + reduce LSD
- Town protected by large sea walls —> prevents flooding + deflect wave energy
- Rock armour in front of sea wall —> reduce energy of destructive waves
